Ion removing system

ABSTRACT

An ion removing system includes an electrolysis apparatus electrolyzing hard water to generate acidic water and alkaline water; and an ion removing apparatus that includes a hard water storage part storing the alkaline water generated by the electrolysis apparatus and a fine bubble generating part generating and supplying fine bubbles to the hard water storage part and that causes the fine bubbles to adsorb metal ions in the alkaline water in the hard water storage part to remove the metal ions from the alkaline water.

TECHNICAL FIELD

The present disclosure relates to an ion removing system BACKGROUND ART

An ion removing system removing metal ions in hard water has hithertobeen disclosed (see, e.g., Patent Document 1).

The ion removing system of Patent Document 1 removes metal ions (calciumions and magnesium ions) in hard water with an ion exchange resin.Specifically, by allowing hard water to flow into a treatment tankincluding an ion exchange resin having sodium ions attached to asurface, the metal ions in the hard water are replaced with the sodiumions to remove the metal ions from the hard water. As a result, thehardness of the hard water is reduced to generate soft water. The metalions present in the hard water are captured on the surface of the ionexchange resin.

PRIOR ART DOCUMENT Patent Document

-   Patent Document 1: JP 2000-140840 A

SUMMARY OF THE INVENTION

Subjects to be Solved by the Invention

However, the ion removing system of Patent Document 1 requires a largeamount of salt water for regenerating the ion exchange resin havingcaptured the metal ions and has a problem of troublesome maintenance.Moreover, a regeneration treatment generates wastewater containing alarge amount of salt water, causing problems of soil pollution and anincreased load on sewage treatment. Furthermore, treated water softenedby an ion removing apparatus has a high concentration of sodium ions andmay not be recommended as drinking water in some regions.

As described above, the ion removing system using an ion exchange resinhas room for improvement from the viewpoints of maintainability andenvironmental properties.

Therefore, an object of the present disclosure is to solve the problemsand to provide an ion removing system in excellent maintainability andenvironmental properties.

Means for Solving the Subjects

To achieve the object, an ion removing system according to an aspect ofthe present disclosure comprises:

an electrolysis apparatus electrolyzing hard water to generate acidicwater and alkaline water; and

an ion removing apparatus that includes a hard water storage partstoring the alkaline water generated by the electrolysis apparatus and afine bubble generating part generating and supplying fine bubbles to thehard water storage part and that causes the fine bubbles to adsorb metalions in the alkaline water in the hard water storage part to remove themetal ions from the alkaline water.

Effect of the Invention

The present disclosure can provide the ion removing system havingexcellent maintainability and environmental properties.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an ion removing system according to afirst embodiment.

FIG. 2 is a schematic for explaining a hypothetical principle ofadsorption of metal ions by the ion removing system according to thefirst embodiment.

FIG. 3 is a schematic for explaining a hypothetical principle ofcrystallization of metal ions by the ion removing system according tothe first embodiment.

FIG. 4 is a schematic for explaining a hypothetical principle of aregeneration treatment by the ion removing system according to the firstembodiment.

FIG. 5A is a diagram showing a schematic configuration of an apparatusused in Experimental Example 1, showing a state after a predeterminedtime has elapsed from generation of fine bubbles.

FIG. 5B is a diagram showing the schematic configuration of theapparatus used in Experimental Example 1, showing a state after apredetermined time has further elapsed from the state shown in FIG. 5A.

FIG. 6 is a diagram showing a result of Experimental Example 1.

FIG. 7 is a schematic for explaining a hypothetical principle ofadsorption of metal ions by an ion removing system according to a secondembodiment.

FIG. 8 is a schematic for explaining a hypothetical principle ofcrystallization of metal ions by the ion removing system according tothe second embodiment.

FIG. 9 is a schematic for explaining a hypothetical principle ofadsorption of metal ions by an ion removing system according to a thirdembodiment.

FIG. 10 is a schematic for explaining a hypothetical principle ofadsorption and crystallization of metal ions by the ion removing systemaccording to the third embodiment.

FIG. 11 is a diagram showing a schematic configuration of an apparatusused in Experimental Examples 2 to 4.

FIG. 12 is a diagram showing a state of a metal component crystallizedin hard water.

FIG. 13A is a graph showing a result of Experimental Example 2, showinga relationship between a mixing percentage of ammonia and acrystallization rate of sample water.

FIG. 13B is a graph showing a result of Experimental Example 2, showinga relationship between pH of the sample water and the crystallizationrate of the sample water.

FIG. 14A is a graph showing a result of Experimental Example 3, showinga relationship between an operating time of a pump and thecrystallization rate of the sample water.

FIG. 14B is a graph showing a result of Experimental Example 3, showinga relationship between the operating time of the pump and the Cahardness of the sample water.

FIG. 14C is a graph showing a result of Experimental Example 3, showinga relationship between the operating time of the pump and the pH of thesample water.

FIG. 15A is a graph showing a result of Experimental Example 4, showinga relationship between the operating time of the pump and thecrystallization rate of the sample water.

FIG. 15B is a graph showing a result of Experimental Example 4, showinga relationship between the operating time of the pump and the Cahardness of the sample water.

FIG. 15C is a graph showing a result of Experimental Example 4, showinga relationship between the operating time of the pump and the pH of thesample water.

FIG. 15D is a graph showing a result of Experimental Example 4, showinga relationship between the operating time of the pump and each of the Cahardness and the total carbonic acid concentration of the sample water.

FIG. 16 is a graph showing a result of Experimental Example 5, showing arelationship between a type of water and a height of bubbles extendingfrom a water surface of evaluation water.

FIG. 17A is a graph showing a result of Experimental Example 6, showinga relationship between time and a crystallization rate of Ca hardness.

FIG. 17B is a diagram showing a result of Experimental Example 6, whichis a graph showing a relationship between time and a crystallizationrate of total hardness.

FIG. 18 is a diagram showing a schematic configuration of an apparatusused in Experimental Example 7.

FIG. 19 is a schematic diagram of an ion removing system according to afourth embodiment.

FIG. 20 is a schematic diagram showing a modification of the ionremoving system according to the first embodiment.

MODES FOR CARRYING OUT THE INVENTION

As a result of intensive studies, the present inventors found novelknowledge that removal of metal ions can be promoted by using “finebubbles” not conventionally used in an ion removal technique (softeningtechnique) for removing metal ions from hard water, thereby completingthe following invention.

An ion removing system according to an aspect of the present disclosurecomprises:

an electrolysis apparatus electrolyzing hard water to generate acidicwater and alkaline water; and

an ion removing apparatus that includes a hard water storage partstoring the alkaline water generated by the electrolysis apparatus and afine bubble generating part generating and supplying fine bubbles to thehard water storage part and that causes the fine bubbles to adsorb metalions in the alkaline water in the hard water storage part to remove themetal ions from the alkaline water.

According to this configuration, since the metal ions are removed fromthe hard water by using the fine bubbles, the need for a large amount ofsalt water required for regenerating the ion exchange resin can beeliminated. This can simplify a regeneration treatment to make themaintenance easier. Additionally, since regeneration wastewatercontaining salt water is not generated, soil pollution and a load onsewage treatment can be suppressed to improve environmental properties.Furthermore, concentration of sodium ions is not increased in treatedwater, so that the generated treated water can be used as drinkingwater. Furthermore, since the hard water is electrolyzed to generatealkaline water so that fine bubbles are supplied to the alkaline water,the pH of the hard water can be increased. As a result, the negativecharges present on the surfaces of the fine bubbles are increased toincrease the power of adsorption of the metal ions by the fine bubbles,so that the metal ion removal efficiency can be improved.

The ion removing system may further include an acidic water storage partstoring the acidic water generated by the electrolysis apparatus, anacidic water flow path allowing the acidic water stored in the acidicwater storage part to flow to the ion removing apparatus and anopening/closing valve opening/closing the acidic water flow path.According to this configuration, for example, when the hard waterstorage part is washed, the acidic water stored in the acidic waterstorage part can be allowed to flow as wash water to the hard waterstorage part through the acidic water flow path, so that the acidicwater can effectively be used.

The ion removing system may further include: a primary-side flow pathconnected to the ion removing apparatus to supply the hard water to theion removing apparatus; a separating apparatus connected to the ionremoving apparatus and separating crystals of a metal componentdeposited by crystallizing the metal ions removed from the alkalinewater by the ion removing apparatus; and a secondary-side flow pathconnected to the separating apparatus to take out, from the separatingapparatus, treated water obtained by separating the crystals; and areturn flow path connected to the separating apparatus to return aportion of the treated water containing the crystals to the primary-sideflow path. According to this configuration, the crystals of the metalcomponent can be introduced into the electrolysis apparatus through thereturn flow path, and the metal ions use the surfaces of the crystals asstarting points for bonding to grow the crystals, so that thecrystallization of the metal ions can be promoted. The crystals can beprevented from being dissolved in the treated water. According to theconfiguration, a circulation flow path can be constituted by theprimary-side flow path, the ion removing apparatus, the separatingapparatus, and the return flow path. This circulation flow path canfurther stabilize fluctuations in the flow rate of the liquid flowingfrom the primary-side flow path to the secondary-side flow path tosuppress a reduction in the metal ion removal efficiency. Additionally,by circulating the crystals of the metal component in the circulationflow path, the crystallization of the metal ions can further bepromoted.

The ion removing system may further include a pump causing the hardwater flowing through the primary-side flow path to flow through theelectrolysis apparatus and the ion removing apparatus to the separatingapparatus. According to this configuration, by driving the pump toforcibly circulate the liquid in the circulation flow path, thefluctuations in the flow rate of the liquid can further be stabilized tosuppress a reduction in the metal ion removal efficiency. Additionally,by forcibly circulating the crystals of the metal component in thecirculation flow path, the crystallization of the metal ions can furtherbe promoted.

Further, a closed-system circulation flow path may be made up of theprimary-side flow path, the electrolysis apparatus, the ion removingapparatus, the separating apparatus, and the return flow path. Accordingto this configuration, air can be prevented from being entrapped intothe circulation flow path to further stabilize the fluctuations in theflow rate of the liquid.

The separating apparatus may be a cyclone-type centrifugal separatingapparatus having a tapered inner circumferential surface with a diameterdecreasing downward and causing the alkaline water to spirally flowdownward along the inner circumferential surface so that the crystalsare separated. According to this configuration, since the metal ionshaving a large specific gravity removed from the hard water move towardthe inner circumferential surface due to centrifugal separation, thecrystals of the metal component can be concentrated in the vicinity ofthe inner circumferential surface. Therefore, for example, by disposingan inlet of the secondary-side flow path at a position distant from theinner circumferential surface, the crystals of the metal component canbe prevented from entering the secondary-side flow path.

One end portion of the return flow path may be opened on the innercircumferential surface side of the separating apparatus. According tothis configuration, the crystals of the metal component deposited in thevicinity of the inner circumferential surface of the separatingapparatus can more reliably be taken into the return flow path.

The ion removing apparatus may include a connection flow path connectedto the separating apparatus above the one end portion of the return flowpath. According to this configuration, the crystals of the metalcomponent deposited in the vicinity of the inner circumferential surfaceof the separating apparatus moves downward, so that the crystals canmore reliably be taken into the return flow path.

First to third embodiments according to the present disclosure willhereinafter be described in detail with reference to the drawings.

First Embodiment

FIG. 1 is a diagram showing a schematic configuration of an ion removingsystem 1 according to a first embodiment.

<General Configuration>

The ion removing system 1 according to the first embodiment includes aprimary-side flow path 2, an ion removing apparatus 3, a separatingapparatus 4, and a secondary-side flow path 5.

The primary-side flow path 2 is connected to the ion removing apparatus3. The primary-side flow path 2 is a flow path for supplying hard waterto the ion removing apparatus 3. In the first embodiment, a pump P isdisposed in a connecting portion between the primary-side flow path 2and the ion removing apparatus 3. The pump P functions to cause the hardwater flowing through the primary-side flow path 2 to flow through theion removing apparatus 3 to the separating apparatus 4. The drive of thepump P is controlled by a controller 6.

The primary flow path 2 is provided with an electrolysis apparatus 16electrolyzing hard water to generate acidic water and alkaline water.The electrolysis apparatus 16 includes a discharge flow path 16 a fordischarging the acidic water electrolyzed from the hard water. Since theelectrolysis apparatus 16 separates the acidic water from the hard waterwhile leaving the alkaline water, the pH of the hard water cansubstantially be increased. For example, the pH of the hard water can beincreased to 9 or higher. The electrolysis apparatus 16 may be an alkaliion water purifier having a known structure, for example.

The discharge flow path 16 a is provided with an opening/closing valve17 capable of opening and closing the discharge flow path 16 a. Theopening/closing operation of the opening/closing valve 17 is controlledby the controller 6. A discharge-side backflow prevention mechanism 18is disposed on the discharge flow path 16 a downstream of theopening/closing valve 17 in the discharge direction.

The discharge-side backflow prevention mechanism 18 is a mechanismpreventing the acidic water from flowing back into the electrolysisapparatus 16. The discharge-side backflow prevention mechanism 18 canprevent the acidic water from mixing again into the alkaline waterseparated from the hard water. The discharge-side backflow preventionmechanism 18 is made up of one or more check valves, for example.Alternatively, the discharge-side backflow prevention mechanism 18 maybe made up of a vacuum breaker, for example. Furthermore, thedischarge-side backflow prevention mechanism 18 may be configured toprevent backflow by a spout space disposed at an outlet of the dischargeflow path 16 a.

The ion removing apparatus 3 includes a hard water storage part 3Astoring hard water, and a fine bubble generating part 3B generating andsupplying fine bubbles to the hard water storage part 3A. The ionremoving apparatus 3 is an apparatus causing fine bubbles to adsorbmetal ions in hard water in the hard water storage part 3A and therebyremoving the metal ions from the hard water. In the first embodiment,the hard water storage part 3A stores the alkaline water generated bythe electrolysis apparatus 16. The ion removing device 3 causes the finebubbles to adsorb metal ions in the alkaline water in the hard waterstorage part 3A to remove the metal ions from the alkaline water. Thefine bubble generating part 3B is arranged downstream of the pump P inthe flow direction of the hard water so as to prevent gas from enteringthe pump P.

In the first embodiment, the metal ions are calcium ions (Ca²⁺) ormagnesium ions (Mg²⁺). In the first embodiment, the fine bubbles arebubbles having a diameter of 100 μm or less. The fine bubbles includemicrobubbles (e.g., having a diameter of 1 μm to 100 μm) and nanobubbles(e.g., having a diameter of less than 1 μm). The microbubbles may bebubbles recognizable as those having a bubble diameter on the order ofmicrometers by those skilled in the field of water treatment. Thenanobubbles may be bubbles recognizable as those having a bubblediameter on the order of nanometers by those skilled in the field ofwater treatment. The fine bubbles have properties different fromordinary bubbles, such as long retention time in water, each of bubbleshardly increasing in diameter and less likely to combine with otherbubbles, and a large contact area facilitating a chemical reaction.

The fine bubbles may include bubbles having a diameter of 100 μm or more(such as milli-bubbles) in a small proportion. For example, bubbleshaving a diameter of 100 μm or less in a proportion of 90% or more maybe defined as the fine bubbles. Additionally, conditions such as havinga diameter of 60 μm or less in a proportion of 50% or more and having adiameter of 20 μm or less in a proportion of 5% or more may be added.When the diameter of bubbles (bubble diameter) is measured, for example,hard water containing fine bubbles may directly be photographed by ahigh-speed camera, and the bubble diameter may be calculated by athree-point method through image processing or may be measured by anyother method. The timing of measuring the bubble diameter may be anytiming as long as the fine bubbles are retained at the time. Examples ofconditions of the measuring method using a high-speed camera describedabove are as follows.

-   -   High-speed camera: FASTCAM 1024 PCI (Photron)    -   Lens system: Z16 APO (Leica)    -   Objective lens: Planapo 2.0× (Leica)    -   Shooting speed: 1000 fps    -   Shutter speed: 1/505000 sec    -   Image area: 1024×1024 pixels (microbubble shooting area: 1.42        mm×1.42 mm, milli-bubble shooting area: 5.69 mm×5.69 mm)    -   Image processing software: Image-Pro Plus (Media Cybermatics)

In the first embodiment, an ion removal gas supply part 7 and asolubilizer supply part 8 are connected via a gas switching mechanism 9to the fine bubble generating part 3B.

The ion removal gas supply part 7 is configured to supply an ion removalgas for removing metal ions in hard water to the fine bubble generatingpart 3B. In the first embodiment, the ion removal gas supply part 7 isconfigured to supply “air” as the ion removal gas to the fine bubblegenerating part 3B. The ion removal gas supply part 7 may include a tankfilled with the ion removal gas, for example. The ion removal gas supplypart 7 may be an apparatus generating the ion removal gas. Furthermore,the ion removal gas supply part 7 may be an apparatus connected to anion removal gas supply source.

The solubilizer supply part 8 is configured to supply a dissolution gas,which is an example of a solubilizer dissolving crystals of a metalcomponent deposited by crystallizing the metal ions removed from thehard water, to the fine bubble generating part 3B. In the firstembodiment, the solubilizer supply part 8 is configured to supply“carbon dioxide (CO₂)” as the dissolution gas to the fine bubblegenerating part 3B. The solubilizer supply part 8 is disposed upstreamof the separating apparatus 4 in the flow direction of the hard water sothat the solubilizer can be supplied to the separating apparatus 4. Thesolubilizer supply part 8 may include a tank filled with thesolubilizer, for example. The solubilizer supply part 8 may be anapparatus generating the solubilizer. Furthermore, the solubilizersupply part 8 may be an apparatus connected to a solubilizer supplysource.

The gas switching mechanism 9 is a mechanism switched to supply eitherthe ion removal gas or the dissolution gas to the fine bubble generatingpart 3B. By switching the gas switching mechanism 9, a softeningtreatment with the ion removal gas and a regeneration treatment with thedissolution gas can selectively be performed. The gas switchingmechanism 9 is made up of one or more valves, for example. The switchingoperation of the gas switching mechanism 9 is controlled by thecontroller 6.

When the gas switching mechanism 9 is switched to supply the ion removalgas, the fine bubble generating part 3B generates the fine bubblescontaining the ion removal gas. The fine bubbles remove the metal ionsfrom the hard water and separate the crystals of the metal component,and the hard water is thereby subjected to the softening treatment. Theprinciple of the softening treatment will be described in detail later.

On the other hand, when the gas switching mechanism 9 is switched tosupply the dissolution gas, the fine bubble generating part 3B generatesthe fine bubbles containing the dissolution gas. The fine bubbles candissolve the crystals of the metal component adhering to the separatingapparatus 4 to perform the regeneration treatment as described later.The principle of the regeneration treatment will be described in detaillater.

The separating apparatus 4 is connected to the ion removing apparatus 3via a connection flow path 3C disposed on an upper outer circumferentialportion of the hard water storage part 3A. The separating apparatus 4 isan apparatus separating the crystals of the metal component deposited bycrystallizing the metal ions removed from the hard water by the ionremoving apparatus 3. The ion removing apparatus 3 and the separatingapparatus 4 can reduce the concentration (hardness) of the metal ions inthe hard water to a predetermined concentration or less to produce softwater. For the definition of hard water and soft water, for example, thedefinition of WHO may be used. Specifically, the soft water may bedefined as water having a hardness of less than 120 mg/L, and the hardwater may be defined as water having a hardness of 120 mg/L or more.

In the first embodiment, the separating apparatus 4 is a cyclone-typecentrifugal separating apparatus having a tapered inner circumferentialsurface 4Aa with a diameter decreasing downward and causing hard waterto spirally flow downward along the inner circumferential surface 4Aa sothat the crystals of the metal component are separated. In the firstembodiment, the separating apparatus 4 includes a separating part 4Ahaving the inner circumferential surface 4Aa and a crystal storage part4B storing crystals of a metal component.

The connection flow path 3C is connected to the separating part 4A suchthat water having passed through the ion removing apparatus 3 isdischarged in a direction eccentric from a central axis of theseparating part 4A. Such an eccentric arrangement allows the waterdischarged into the separating part 4A to flow spirally downward alongthe inner circumferential surface 4Aa. The metal ions having a largespecific gravity removed from the hard water move toward the innercircumferential surface 4Aa due to centrifugal separation and aredeposited as the crystals of the metal component in the vicinity of theinner circumferential surface 4Aa. A portion of the crystals adheres tothe inner circumferential surface 4Aa.

The crystal storage part 4B is disposed below the separating part 4A.The crystal storage part 4B includes a discharge flow path 4Ba fordischarging water containing the crystals of the metal component. Thedischarge flow path 4Ba is provided with an opening/closing valve 10capable of opening and closing the discharge flow path 4Ba. Theopening/closing operation of the opening/closing valve 10 is controlledby the controller 6. A discharge-side backflow prevention mechanism 11is disposed on the discharge flow path 4Ba downstream of theopening/closing valve 10 in a discharge direction.

The discharge-side backflow prevention mechanism 11 is a mechanismpreventing the crystals of the metal component from flowing back intothe separating apparatus 4. The discharge-side backflow preventionmechanism 11 can prevent the crystals of the metal component from mixingagain into treated water (soft water) obtained by separating thecrystals of the metal component from hard water. The discharge-sidebackflow prevention mechanism 11 is made up of one or more check valves,for example. Alternatively, the discharge-side backflow preventionmechanism 11 may be made up of a vacuum breaker, for example.Furthermore, the discharge-side backflow prevention mechanism 11 may beconfigured to prevent backflow by a spout space disposed at an outlet ofthe discharge flow path 4Ba.

The secondary-side flow path 5 is connected to the separating apparatus4. The secondary-side flow path 5 is a flow path for taking out from theseparating apparatus 4 the treated water obtained by separating thecrystals of the metal component. In the first embodiment, since theseparating apparatus 4 is a cyclone-type centrifugal separatingapparatus, the crystals of the metal component can be concentrated inthe vicinity of the inner circumferential surface 4Aa. To prevent thecrystals of the metal component from entering the secondary-side flowpath 5, the secondary-side flow path 5 is connected to an upper centralportion of the separating part 4A at a position distant from the innercircumferential surface 4Aa.

The treated water flowing through the secondary-side flow path 5 issupplied to a kitchen, a bathroom, a toilet, or a lavatory, for example.If a flow rate of liquid flowing from the primary-side flow path 2 tothe secondary-side flow path 5 is drastically reduced due to use of thetreated water, a speed of centrifuging the metal ions from the hardwater may decrease, and the metal ion removal efficiency may be reduced.Additionally, the crystals of the metal component may be mixed in thetreated water.

Therefore, in the first embodiment, a return flow path 12 is connectedto the separating apparatus 4 and the primary-side flow path 2 so as toreturn to the primary-side flow path 2 a portion of the treated waterobtained by separating the crystals of the metal component from the hardwater by the separating apparatus 4. Specifically, the primary-side flowpath 2, the ion removing apparatus 3, the separating apparatus 4, andthe return flow path 12 constitute a circulation flow path. Thiscirculation flow path can further stabilize fluctuations in the flowrate of the liquid flowing from the primary-side flow path 2 to thesecondary-side flow path 5 to suppress a reduction in the metal ionremoval efficiency. By driving the pump P to forcibly circulate theliquid in the circulation flow path, the fluctuations in the flow rateof the liquid can further be stabilized to suppress a reduction in themetal ion removal efficiency. The crystals of the metal component can beprevented from mixing into the treated water.

The flow rate of the liquid flowing through the circulation flow path ispreferably equal to or greater than the flow rate of the soft water used(e.g., 2 liters/minute). When the flow rate of the liquid flowingthrough the circulation flow path is larger than the flow rate of thesoft water used, the fluctuations in the flow rate of the liquid can bemade more stable, and the soft water can stably be produced. Thecirculation flow path is preferably a closed system. As a result, aircan be prevented from being entrapped into the circulation flow path tofurther stabilize the fluctuations in the flow rate of the liquid.

In the first embodiment, one end portion 12 a of the return flow path 12is opened on the central axis side of the separating part 4A. Thisprevents the crystals of the metal component deposited in the vicinityof the inner circumferential surface 4Aa from entering the return flowpath 12. The connection flow path 3C of the ion removing apparatus 3 isconnected to the separating part 4A below the one end portion 12 a ofthe return flow path 12. Therefore, the one end part 12 a of the returnflow path 12 is located above an outlet of the connection flow path 3Cfrom which the hard water after removal of the metal ions is spirallydischarged downward. As a result, the crystals of the metal componentdeposited in the vicinity of the inner circumferential surface 4Aa arefurther prevented from entering the return flow path 12.

The primary-side flow path 2 is provided with a supply-side backflowprevention mechanism 13. The supply-side backflow prevention mechanism13 is a mechanism preventing the fine bubbles and the treated water fromflowing back to the hard water supply side. The supply-side backflowprevention mechanism 13 is made up of one or more check valves, forexample. In the first embodiment, the supply-side backflow preventionmechanism 13 is disposed on the primary-side flow path 2 upstream of thereturn flow path 12 in the flow direction of the hard water. As aresult, the fine bubbles, the treated water, etc. can more reliably beprevented from flowing back to the hard water supply side.

For example, when maintenance is required due to a failure of the ionremoving apparatus 3, water cannot be used during the maintenance.Therefore, in the first embodiment, the primary-side flow path 2 and thesecondary-side flow path 5 are connected by a bypass flow path 14. Theion removing system 1 includes a flow switching mechanism switching theflow direction of the hard water flowing through the primary-side flowpath 2 to either the ion removing apparatus 3 or the bypass flow path14. Since the flow switching mechanism can be switched to cause the hardwater flowing through the primary-side flow path 2 to flow through thebypass flow path 14 to the secondary-side flow path 5, the hard watercan be used even during maintenance. Even not during maintenance, theflow switching mechanism can be switched to selectively use the hardwater and the treated water (soft water).

In the first embodiment, the flow switching mechanism includes a firstvalve 15A capable of opening and closing the primary-side flow path 2, asecond valve 15B capable of opening and dosing the secondary-side flowpath 5, and a third valve 15C capable of opening and closing the bypassflow path 14. The opening/dosing operations of the first valve 15A, thesecond valve 15B, and the third valve 15C are controlled by thecontroller 6.

The controller 6 is configured to selectively provide a first control ofopening the first valve 15A and the second valve 15B and closing thethird valve 15C, and a second control of closing the first valve 15A andthe second valve 15B and opening the third valve 15C. When thecontroller 6 provides the first control, the hard water flowing throughthe primary-side flow path 2 flows to the ion removing apparatus 3 andis subjected to the softening treatment before flowing into thesecondary-side flow path 5. As a result, the treated water (soft water)is discharged to an outlet of the secondary-side flow path 5. When thecontroller 6 provides the second control, the hard water flowing throughthe primary-side flow path 2 flows through the bypass flow path 14 intothe secondary-side flow path 5. As a result, the hard water isdischarged to the outlet of the secondary-side flow path 5. Therefore,the controller 6 can provide the first control or the second control toselectively discharge the hard water or the treated water (soft water)from the outlet of the secondary-side flow path 5.

<Softening Treatment>

The principle of the softening treatment using fine bubbles will bedescribed in more detail.

It is presumed that supplying fine bubbles containing air into hardwater causes actions described in the following sections (1) and (2) onthe metal ions in the hard water. Specifically, it is presumed that themetal ions in the hard water can be adsorbed to the fine bubbles andthat the adsorbed metal ions can be crystallized to remove crystals of ametal component from the hard water. More specifically, the principlewill be described as follows. It is noted that the present disclosure isnot bound to the specific principles described in the following sections(1) and (2).

(1) Adsorption of Metal Ions

As shown in FIG. 2, when the fine bubbles containing air are suppliedinto the hard water, H⁺ (hydrogen ions) and OH⁻ (hydroxide ions) aremixed on surfaces of the fine bubbles, and H⁺ is positively charged,while OH⁻ is negatively charged (only OH⁻ is shown in FIG. 2). On theother hand, the hard water has Ca²⁺ and Mg²⁺ present as the positivelycharged metal ions.

Ca²⁺ having a positive charge is adsorbed by OH⁻ present on the surfacesof the fine bubbles due to an action of an intermolecular force(interionic interaction). Ca²⁺ can be adsorbed to the fine bubbles inthis way. Although H⁺ repelling Ca²⁺ is present on the surfaces of thefine bubbles, it is probable that OH⁻ acts in preference to H⁺ andadsorbs Ca²⁺. This “adsorption of metal ions” is mainly performed in theion removing apparatus 3.

In the first embodiment, the electrolysis apparatus 16 separates theacidic water from the hard water while leaving the alkaline water, sothat the pH of the hard water is increased. As the pH of the hard waterrises, negatively charged OH⁻ present on the surfaces of the finebubbles increases, and Ca²⁺ is more easily adsorbed to the fine bubbles.As a result, the crystallization of metal ions can be promoted asdescribed later.

(2) Crystallization of Metal Ions

In addition to the reaction shown in FIG. 2, a reaction shown in FIG. 3is promoted by supplying the fine bubbles containing air into the hardwater. Specifically, unlike ordinary bubbles, the fine bubbles suppliedinto the hard water hardly float to the surface, dissolve into the hardwater, and therefore gradually shrink as shown in FIG. 3 due to anincrease in surface tension. As described above, Ca²⁺ is adsorbed on thesurfaces of the fine bubbles. More specifically, Ca²⁺ is present ascalcium ions of soluble Ca(HC₃)₂ (calcium hydrogencarbonate). As thefine bubbles gradually shrink, the dissolved concentration of Ca²⁺ onthe surfaces of the fine bubbles increases. The increase in thedissolved concentration results in a supersaturation state at a certainpoint, and Ca²⁺ is crystallized and deposited. This is represented by aspecific chemical formula as in Formula 1 below.

Ca(HCO₃)₂→CaCO₃+CO₂+H₂O  (Formula 1)

CaCO₃ (calcium carbonate) is insoluble (water-insoluble) and istherefore deposited as crystals of a metal component. As a result, thosedissolved as Ca²⁺ of Ca(HCO₃)₂ are deposited as crystals of the metalcomponent. By promoting such a reaction, CaCO₃ deposited bycrystallizing the metal ions Ca²⁺ can be separated from the hard water.This “crystallization of metal ions” is mainly performed in theseparating part 4A of the separating apparatus 4.

Although a reaction may occur in the reverse direction of Formula 1 inthe same water, it is presumed that the reaction in the direction ofFormula 1 is preferentially performed in the equilibrium relationship bycontinuously supplying the fine bubbles.

In the first embodiment, since the separating apparatus 4 is acyclone-type centrifugal separating apparatus, the crystals of the metalcomponent are deposited in the vicinity of the inner circumferentialsurface 4Aa of the separating part 4A and stored in the crystal storagepart 4B. The crystals of the metal component stored in the crystalstorage part 4B are discharged through the discharge flow path 4Ba byopening the opening/closing valve 10. By separating the crystals of themetal component from inside the hard water in this way, the hard watercan be softened.

<Regeneration Treatment>

The principle of the regeneration treatment using fine bubbles will bedescribed in more detail.

By performing the softening treatment, a portion of CaCO₃ deposited bycrystallizing the metal ions adheres to the inner circumferentialsurface 4Aa of the separating part 4A. The regeneration treatment isperformed as a treatment for returning CaCO₃ to Ca(HCO₃)₂. Specifically,the fine bubble generating part 3B generates fine bubbles containingcarbon dioxide, which is a gas different from that used during thesoftening treatment.

As shown in FIG. 4, by supplying the fine bubbles of carbon dioxide toCaCO₃ adhering to the inner circumferential surface 4Aa of theseparating part 4A, the following reaction is promoted.

CaCO₃+CO₂+H₂O→Ca(HCO₃)₂  (Formula 2)

The reaction generates soluble (water-soluble) Ca(HCO₃)₂ from insolubleCaCO₃. Ca(HCO₃)₂ dissolves into water and moves to the crystal storagepart 4B. The Ca(HCO₃)₂ having moved to the crystal storage part 4B isdischarged through the discharge flow path 4Ba by opening theopening/closing valve 10. As a result, the insoluble CaCO₃ adhering tothe inner circumferential surface 4Aa of the separating part 4A can bedischarged to the outside to restore the original state. Subsequently,the softening treatment described above can be performed again.

Although Ca²⁺ is described as an example of the metal ions in the abovedescription, it is presumed that the same reaction occurs with Mg².

As described above, when the metal ions are removed from hard water byusing an ion exchange resin, a large amount of salt water is requiredfor regenerating the ion exchange resin. In this regard, the ionremoving system 1 of the first embodiment removes the metal ions fromthe hard water by using the fine bubbles and therefore can eliminate theneed for a large amount of salt water required for regenerating the ionexchange resin. This can simplify the regeneration treatment to make themaintenance easier. Additionally, since regeneration wastewatercontaining salt water is not generated, soil pollution and a load onsewage treatment can be suppressed to improve environmental properties.Furthermore, concentration of sodium ions is not increased in treatedwater, so that the generated treated water can be used as drinkingwater. Furthermore, since the hard water is electrolyzed to generatealkaline water, and the fine bubbles are supplied to the alkaline waterin this configuration, the pH of the hard water can be increased. As aresult, the negative charges present on the surfaces of the fine bubblesare increased to increase the power of adsorption of the metal ions bythe fine bubbles, so that the metal ion removal efficiency can beimproved.

Additionally, the ion removing system 1 of the first embodiment uses airas the ion removal gas and therefore can suppress the cost required forgenerating the fine bubbles to an extremely low level.

Furthermore, the ion removing system 1 of the first embodiment performsthe regeneration treatment by supplying the fine bubbles of carbondioxide as the dissolution gas after removal of the metal ions. This canpromote the reaction of generating soluble Ca(HCOs)₂ from insolubleCaCO₃ to promote the regeneration treatment.

Experimental Example 1

Experimental Example 1 performed to confirm the principle of thesoftening treatment using fine bubbles will be described. Experimentswere conducted by using an apparatus 20 shown in FIGS. 5A and 5B.

FIGS. 5A and 5B are diagrams showing a schematic configuration of theapparatus 20 used in Experimental Example 1. FIG. 5A shows a state aftera predetermined time has elapsed (specifically, after 15 seconds haveelapsed) from generation of fine bubbles, and FIG. 5B shows a stateafter a predetermined time has further elapsed (specifically, after 45seconds have elapsed) from the state shown in FIG. 5A. The state of FIG.5A corresponds to a state when the elapsed time from the generation offine bubbles is 15 seconds in FIG. 6, and the state of FIG. 5Bcorresponds to a state when the elapsed time from the generation of finebubbles is 60 seconds in FIG. 6.

The apparatus 20 shown in FIGS. 5A and 5B is an experimental apparatuscapable of supplying fine bubbles 23 from the bottom surface side in awater tank 22 (hard water storage part) storing a hard water 21. In theapparatus 20, the concentration of metal ions in the hard water 21 canbe measured at two positions on the bottom surface side and the watersurface side. When the apparatus 20 as described above was used tosupply the fine bubbles 23 into the water tank 22 and concentrationtransitions of metal ions were detected on the bottom surface side andthe water surface side, results shown in FIG. 6 were obtained.

From the results shown in FIG. 6, the effect of “adsorption of metalions by fine bubbles” described above was demonstrated. Specific resultswill be described later.

As shown in FIGS. 5A and 5B, the apparatus 20 includes the water tank22, a gas supply part 24, a first piping 25, a fine bubble generatingpart 26, a second piping 27, a pump 28, a first water intake part 30, asecond water intake part 32, and a metal ion concentration detector 34.

The water tank 22 is a water tank storing the hard water 21. In theexample shown in FIGS. 5A and 5B, the water tank 22 is configured as atank elongated in a vertical direction. The gas supply part 24 is amember supplying a gas to the fine bubble generating part 26 via thefirst piping 25. The fine bubble generating part 26 is an apparatusgenerating the fine bubbles 23 from the gas supplied from the gas supplypart 24. The fine bubble generating part 26 corresponds to the finebubble generating part 3B described above. The gas is supplied from thegas supply part 24 to the fine bubble generating part 26 due to anaction of negative pressure from the pump 28 via the second piping 27.

The first water intake part 30 is a member taking sample water of thehard water 21 from near a bottom surface 22 a of the water tank 22. Thesecond water intake part 32 is a member taking sample water from near awater surface 22 b of the water tank 22. The height positions of thefirst water intake part 30 and the second water intake part 32 may beset to any positions, and a distance D1 from the first water intake part30 to the second water intake part 32 can be adjusted to a desiredvalue.

In the example shown in FIGS. 5A and 5B, the height position of thefirst water intake part 30 is set to substantially the same position asthe height position where the fine bubble generating part 26 generatesthe fine bubbles 23.

The metal ion concentration detector 34 is a member detecting theconcentration of metal ions in the sample water taken from the firstwater intake part 30 and the second water intake part 32.

When the fine bubble generating part 26 and the pump 28 are operated inthe configuration, the gas is sent from the gas supply part 24 via thefirst piping 25 to the fine bubble generating part 26 due to the actionof negative pressure from the pump 28 via the second piping 27. The finebubble generating part 26 uses this gas as a raw material to generateand supply the fine bubbles 23 to the water tank 22 (arrow A1 of FIG.5A).

The fine bubble generating part 26 and the pump 28 are operated for apredetermined period (15 seconds in Experimental Example 1) tocontinuously generate the fine bubble 23.

Subsequently, the operation of the fine bubble generating part 26 andthe pump 28 is stopped. The stop of the operation is followed by apredetermined resting period (45 seconds in Experimental Example 1).

As shown in FIG. 5A, at the end of the operating period (after 15seconds from the generation of the fine bubbles), it was visuallyconfirmed that the fine bubbles 23 supplied into the water tank 22 movedupward in the hard water 21 (arrow A2) and were retained in a lowerportion of the water tank 22.

As shown in FIG. 5B, at the end of the resting period (after 60 secondsfrom the generation of fine bubbles), it was visually confirmed that thefine bubbles 23 supplied into the hard water 21 further moved upward toreach the water surface 22 b (arrow A3) and were retained in an upperportion of the water tank 22.

The sample water was extracted from the first water intake part 30 andthe second water intake part 32 at a predetermined timing during theoperation to measure the metal ion concentration with the metal ionconcentration detector 34, and the results are shown in FIG. 6.

Specific experimental conditions related to the results of FIG. 6 arelisted below.

Experimental Conditions

-   -   Type of gas supplied by the gas supply part 24: air    -   Hardness of the hard water 21: about 300 mg/L    -   Temperature of the hard water 21: 25° C.    -   Distance D1 from the first water intake part 30 to the second        water intake part 32: about 1 m    -   Operating period of the fine bubble generating part 26 and the        pump 28: 15 seconds    -   Resting period of the fine bubble generating part 26 and the        pump 28: 45 seconds    -   Metal ion concentration detector 34: LAQUA F-70 manufactured by        HORIBA, Ltd.    -   Metal ion to be measured: Ca²⁺    -   Sample water extraction timing: after 0 seconds, 15 seconds, 30        seconds, 60 seconds from the start of operation

In FIG. 6, the horizontal axis represents an elapsed time (seconds) fromthe generation of fine bubbles, and the vertical axis represents aconcentration transition (%) of metal ions (Ca⁻) detected by the metalion concentration detector 34. The concentration transition of the metalions represents the transition of the metal ion concentration when themetal ion concentration measured at the start of operation is 100%.

As shown in FIG. 6, the concentration in the sample water extracted fromthe first water intake part 30 near the bottom surface 22 a of the watertank 22 increases to about 108% when 15 seconds have elapsed. During thesubsequent resting period, the concentration gradually decreases andfinally decreases to about 97%.

On the other hand, the concentration in the sample water extracted fromthe second water intake part 32 near the water surface 22 b of the watertank 22 is maintained at nearly 100% until 15 seconds have elapsed, thengradually increases during the resting period, and finally increases toabout 115%.

The results of the concentration transitions of the metal ions and thebehavior of the fine bubbles 23 are associated with each other asfollows.

When 15 seconds have elapsed as shown in FIG. 5A, the metal ionconcentration is increased in the sample water of the first water intakepart 30 in which the fine bubbles 23 are retained. On the other hand,the metal ion concentration is almost not changed in the sample water ofthe second water intake part 32 in which the fine bubbles 23 are notretained.

When 60 seconds have elapsed as shown in FIG. 5B, the metal ionconcentration is reduced to a little less than 100% in the sample waterof the first water intake part 30 in which the fine bubbles 23 are notretained. On the other hand, the metal ion concentration issignificantly increased in the sample water of the second water intakepart 32 in which the fine bubbles 23 are retained.

From the results as described above, it is presumed that the metal ionsCa²⁺ in the hard water 21 are adsorbed to the fine bubbles 23 and moveupward together with the fine bubbles 23 going up.

Based on the presumption, the effect of “adsorption of metal ions byfine bubbles” described above was demonstrated.

Second Embodiment

An ion removing system according to a second embodiment of the presentdisclosure will be described. In the second embodiment, differences fromthe first embodiment will mainly be described. In the second embodiment,the same or equivalent constituent elements as the first embodiment aredenoted by the same reference numerals. In the second embodiment, thedescription overlapping with the first embodiment will not be made.

The second embodiment is different from the first embodiment in thatnitrogen is used instead of air as the gas of the fine bubbles in thesoftening treatment.

It is presumed that by generating and supplying the fine bubbles ofnitrogen from the fine bubble generating part 3B into hard water,actions described in the following sections (3), (4) are promoted inaddition to “(1) Adsorption of Metal Ions” and “(2) Crystallization ofMetal Ions” described above. It is noted that the present disclosure isnot bound to the specific principles described in the following sections(3), (4).

(3) Promotion of Adsorption of Metal Ions

As shown in FIG. 7(a), H⁺ and OH⁻ are charged around the fine bubbles.As described above, positively charged Ca²⁺ is adsorbed to negativelycharged OH⁻. When nitrogen is used as the fine bubbles under suchcircumstances, a reaction of Formula 3 is promoted.

N₂+6H⁺+6e ⁻→2NH₃

NH₃+H₂O→NH₄ ⁺+OH⁻  (Formula 3)

As shown in FIG. 7(b), the number of H⁺ ions is reduced relative to thenumber of OH⁻ ions by promoting the reaction of Formula 3. As a result,a negative charge becomes strong in terms of the fine bubbles, so thatCa²⁺ having a positive charge is easily adsorbed.

When nitrogen is used as in the second embodiment, the reaction ofFormula 3 can be promoted as compared to when air is used as in thefirst embodiment, so that the adsorption of the metal ions is furtherpromoted. As a result, the metal ions can be separated and removed inlarger amount from hard water.

The principle is presumed to be applicable not only to nitrogen but alsoto any gas that can react with H⁺ ions to reduce the number of H⁺ ionsrelative to the number of OH⁻ ions.

(4) Promotion of Crystallization of Metal Ions

Since nitrogen is an inert gas different from air, when nitrogen issupplied into hard water, balance of partial pressure is lost in the gascontained in the hard water. This promotes a reaction as shown in FIG.8.

As shown in FIG. 8, another gas component dissolved in hard water actson the fine bubbles composed of nitrogen to replace nitrogen. In theexample shown in FIG. 8, CO₂ is contained in Ca(HCO₃)₂ present aroundthe fine bubbles, and this CO₂ is extracted and acts to replacenitrogen. Specifically, the following reaction is promoted.

Ca(HCO₃)₂→CaCO₃+CO₂+H₂O  (Formula 4)

As described above, a reaction occurs such that insoluble CaCO₃ isgenerated from soluble Ca(HCO₃)₂. In this case, CO₂ and H₂O aregenerated. CaCO₃ is insoluble and is thereof deposited as crystals of ametal component.

The first metal ions contained as Ca²⁺ of Ca(HCO₃)₂ in the hard watercan be crystallized and deposited by the reaction. As a result, thecrystals of the metal component can be removed from the hard water.

The principle is presumed to be applicable not only to nitrogen but alsoto any gas other than air that can break the balance of partial pressureof the gas dissolved in hard water.

Since the fine bubbles are generated by taking in nitrogen and suppliedinto the hard water in the second embodiment as described above, thereactions described in the sections of “(3) Promotion of Adsorption ofMetal Ions” and “(4) Promotion of Crystallization of Metal lons” can bepromoted as compared to when air is used. This can improve the accuracyof removal of metal ions from the hard water.

Third Embodiment

A method for removing metal ions by an ion removing system according toa third embodiment of the present disclosure will be described. In thethird embodiment, differences from the first and second embodiments willmainly be described, and the description overlapping with the first andsecond embodiments will not be made.

While the fine bubble generating part 3B generates fine bubblescontaining air in the first and second embodiments, the third embodimentis different from the first and second embodiments in that fine bubblescontaining a mixed gas obtained by mixing multiple types of gases aregenerated.

The mixed gas used for generating the fine bubbles in the thirdembodiment is a gas obtained by mixing two types of gases, i.e., a firstgas that is a basic gas and a second gas that is a gas having a propertyof slower dissolution rate than the first gas. Therefore, the ionremoval gas supply part 7 shown in FIG. 1 supplies the mixed gasobtained by mixing the first gas and the second gas, as the ion removalgas to the fine bubble generating part 3B.

It is presumed that by generating the fine bubbles with the mixed gascontaining the first gas and the second gas, actions described in thefollowing sections (5), (6) are promoted in addition to “(1) Adsorptionof Metal Ions” and “(2) Crystallization of Metal Ions” described above.It is noted that the present disclosure is not bound to the specificprinciples described in the following sections (5), (6).

(5) Potential Change on Surfaces of Fine Bubbles Due to First Gas

The first gas contained in the mixed gas is a basic gas receiving H⁺ inan acid-base reaction. The first gas dissolves in water to generate OH.Specifically, the reaction of Formula 5-1 occurs.

X+H₂O→XH⁺+OH⁻  (Formula 5-1)

In Formula 5-1, the first gas is represented by Chemical Formula X. Whenthe reaction of Formula 5-1 occurs, as shown in FIG. 9, the proportionof OH⁻ present around fine bubbles 40 increases as compared to theproportion of H⁺ (H⁺ is not shown in FIG. 9). A potential of asolid-liquid interface strongly depends on pH in water quality since H⁺and OH⁻ in water are potential-determining ions, and a positive chargebecomes stronger as H⁺ increases while a negative charge becomesstronger as OH⁻ increases. As a result, a negative charge becomes strongin terms of the fine bubbles 40, so that Ca²⁺ having a positive chargeis easily adsorbed. In this way, the metal ion adsorption effect of thefine bubbles 40 can be improved.

Furthermore, in the third embodiment, the basic gas of ammonia is usedas the first gas. When ammonia is used, Formula 5-1 is specificallydescribed as in Formula 5.

NH₃+H₂O→NH₄ ⁺+OH⁻  (Formula 6)

By generating the fine bubbles 40 using ammonia, which is a versatilegas having high solubility in water, the generation cost of the finebubbles 40 can be reduced while the metal ion adsorption effectdescribed above is improved.

The principle is presumed to be applicable not only to ammonia but alsoto any basic gas. Examples of such a basic gas include methylamine,ethylamine, propylamine, isopropylamine, butylamine, hexylamine,cyclohexylamine, dimethylamine, diethylamine, diisopropylamine,dipropylamine, di-n-butylamine, ethanolamine, diethylethanolamine,dimethylethanolamine, ethylenediamine, dimethylaminopropylamine,N,N-dimethylethylamine, trimethylamine, triethylamine,tetramethylenediamine, diethylenetriamine, propyleneimine,pentamethylenediamine, hexamethylenediamine, morpholine,N-methylmorpholine, and N-ethylmorpholine.

As shown in Formula 5-1, X is not limited to a basic gas, and it isprobable that the same effect is produced as long as X is a “hydroxylion donating gas” reacting with water (H₂O) to donate a hydroxyl ion(OH⁻). Examples of the hydroxyl ion donating gas include a soluble ozonegas (O₃). When the ozone gas is supplied to water, the reactionrepresented by Formula 5-2 similar to Formula 5-1 probably occurs.

O₃+H₂O+2e ⁻→O₂+2OH⁻  (Formula 5-2)

According to Formula 5-2, it is probable that the hydroxyl ion donatinggas “X” causing the reaction represented by Formula 5-3 produces thesame effect.

XO+H₂O+2e ⁻→X+2OH⁻  (Formula 5-3)

Ozone will be described in Experimental Example 6.

(6) Maintenance of Fine Bubbles with Second Gas

As described in the section of “(5) Potential Change on Surfaces of FineBubbles Due to First Gas”, the first gas is the basic gas contained inthe mixed gas and dissolves in water to increase the proportion of OH⁻on the surfaces of the fine bubbles 40. Such a first gas is mixed withthe second gas that is a gas having a property of slower dissolutionrate than the first gas. By mixing with such a second gas, the finebubbles 40 are prevented from being entirely dissolved in water evenwhen the first gas is dissolved in water, so that the state of the finebubbles 40 can be maintained. By maintaining the state of the finebubbles 40, the adsorption effect on Ca²⁺ ions attributable to the finebubbles described in the first and second embodiments can be maintained.

In the third embodiment, nitrogen is used as the second gas. Bygenerating the fine bubbles 40 using nitrogen, which is a versatile gasharmless to the human body, the generation cost of the fine bubbles 40can be reduced while safety is secured. Moreover, since nitrogen is anon-water-soluble gas (non-soluble gas), the effect of maintaining thestate of the fine bubbles 40 can more effectively be exerted.

The principle is presumed to be applicable not only to nitrogen but alsoto any gas having a property of slower dissolution rate than the firstgas, which is a basic gas. When the second gas is selected, a gas to beselected may be a gas having a rate of dissolution (solubility) intowater slower (lower) than the first gas under the same conditionsincluding temperature and pressure conditions. Examples of such a secondgas include nitrogen, hydrogen, carbon monoxide, butane, oxygen,methane, propane, ethane, nitric oxide, ethylene, propene, acetylene,and carbon dioxide in ascending order of solubility. Among them, when anon-water-soluble gas such as nitric oxide, oxygen, or hydrogen is used,the effect of maintaining the state of the fine bubbles 40 can moreeffectively be exerted.

It has been described in the sections of “(3) Promotion of Adsorption ofMetal Ions” and “(4) Promotion of Crystallization of Metal Ions” thatnitrogen dissolves into hard water with reference to FIGS. 7 and 8, andthis reaction probably occurs at the same time. Nitrogen is insoluble inwater and therefore difficult to dissolve in water so that a strongeffect of maintaining the state of the fine bubbles 40 is exerted;however, no small amount of nitrogen dissolves in water. Therefore, thephenomenon of dissolution of nitrogen into water described in thesections of “(3) Promotion of Adsorption of Metal Ions” and “(4)Promotion of Crystallization of Metal Ions” occurs to no small extentsimultaneously with the phenomenon of maintenance of the fine bubbleswith nitrogen described in the section of “(6) Maintenance of FineBubbles with Second Gas”.

As described above, the fine bubble generating part of the thirdembodiment generates the fine bubbles 40 from a mixed gas obtained bymixing the first gas reacting with water to donate hydroxyl ions and thesecond gas having a property of slower dissolution rate than the firstgas. The first gas is a hydroxyl ion donating gas and reacts with waterto increase the proportion of OH⁻ on the surfaces of the fine bubbles40. This can increase the effect of adsorbing metal ions such as Ca²⁺ tothe fine bubbles 40. Furthermore, by mixing the second gas having aproperty of slower dissolution rate than the first gas, the fine bubbles40 can be prevented from being completely dissolved in water to maintainthe state of the fine bubbles 40.

In the third embodiment, the first gas is a soluble basic gas (ammonia).Since the first gas is a basic gas and is first dissolved in water, andthe second gas having a property of slower dissolution rate than thebasic gas is negatively charged, the effect can be achieved by utilizinga difference in dissolution rate between the two gases.

Mixing proportions of ammonia and nitrogen in the fine bubbles 40 may beset to any value or may be set, for example, such that the mixingproportion of nitrogen to ammonia becomes larger (e.g., ammonia:nitrogenis 1:99 in an amount of substance (volume ratio)). With such a setting,the increase in OH⁻ due to the dissolution of ammonia is limited only ina region near the surfaces of the fine bubbles 40, and the proportion ofOH⁻ hardly changes at a position distant from the fine bubbles 40. Thiscan keep the water quality of the entire water unchanged while causing achange only in the vicinity of the surfaces of the fine bubbles 40. Onthe other hand, by increasing the proportion of nitrogen, the state ofthe fine bubbles 40 can be maintained longer. In this way, the effectdescribed above can be produced by setting the amount of substance ofthe second gas, which has a slower dissolution rate than the basic gas,larger than the amount of substance of the first gas, which is the basicgas, in the mixed gas. Since the amount of substance and the volume areproportional to each other under the conditions of the same temperatureand the same pressure, the mixing proportions of the first gas and thesecond gas may be set by using either the amount of substance or thevolume.

Alternatively, the mixing proportions may be set such that the mixingproportion of ammonia to nitrogen becomes larger. With such a setting,the metal ions contained in hard water can further be crystallized andremoved. The principle of promotion of crystallization as describedabove will be described in Experimental Examples 2 to 4.

In the third embodiment, unlike a supply form in which ammonia andnitrogen are separately formed into fine bubbles and the fine bubblesare separately supplied to hard water without being mixed, the finebubbles 40 of the mixed gas obtained by mixing ammonia and nitrogen aresupplied to hard water. Such a supply form can prevent ammonia frombeing dissolved alone at a position distant from the fine bubbles 40, sothat the function of increasing OH⁻ only in the vicinity of the surfacesof the fine bubbles 40 can sufficiently be exerted.

A hypothetical principle will be described in terms of the metal ionadsorption effect of the fine bubbles 40 using the mixed gas obtained bymixing the first gas, which is ammonia, and the second gas, which isnitrogen, described above, in particular, until the metal ions arefinally crystallized, with reference to a schematic of FIG. 10.

As shown in FIG. 10, when the fine bubbles 40 are supplied into hardwater, ammonia is water-soluble and dissolves in surrounding waterbetween ammonia and nitrogen constituting the fine bubbles 40 (ammoniagas dissolution). Therefore, as described in the section of “(5)Potential Change on Surfaces of Fine Bubbles Due to First Gas”, NH isgenerated on the surfaces of the fine bubbles 40 and the proportion ofOH⁻ increases (surface condensation). In this case, the effect ofadsorbing Ca² ions is increased.

When the surface concentration further proceeds, the concentration ofOH⁻ on the surfaces of the fine bubbles 40 is maximized. Specifically,the pH on the surfaces of the fine bubbles 40 is maximized, and the zetapotential of the fine bubbles 40 is maximized (large local pH, largezeta potential).

In the states of “ammonia gas dissolution”, “surface condensation”, and“large local pH, large zeta potential”, Ca²⁺ is adsorbed to the finebubbles 40. In this case, if the fine bubbles 40 with Ca²⁺ adsorbedthereto are separated from the hard water, the metal ions can be removedfrom the hard water.

If the separation is not performed or if the metal ions remain as thefine bubbles 40 even though the separation is performed, crystallizationof Ca²⁺ adsorbed to the surfaces of the fine bubbles 40 starts.Specifically, Ca²⁺ is crystallized and deposited as crystals 42.Additionally, as the crystals 42 are deposited, the fine bubbles 40starts disappearing (disappearance).

As the crystallization of Ca²⁺ and the disappearance of the fine bubbles40 proceed, water-insoluble nitrogen maintaining the state of the finebubbles 40 diffuses into water as a dissolved gas (dissolved gasdiffusion).

In the states of “disappearance” and “dissolved gas diffusion” describedabove, those contained as the metal ions in the hard water are depositedas the crystals 42. By separating the crystals 42 deposited in this wayfrom the hard water, the metal ions in the hard water can becrystallized and removed.

Experimental Examples 2 to 4

Experimental Examples 2 to 4 performed to confirm the influence of themixing proportions of ammonia and nitrogen in the fine bubbles 40 on thecrystallization of the metal component will be described. Experimentswere conducted by using an apparatus 50 shown in FIG. 11.

FIG. 11 is a diagram showing a schematic configuration of the apparatus50 used in Experimental Examples 2 to 4. The apparatus 50 shown in FIG.11 includes a mixed gas supply part 52, a treatment tank 54, a firstpiping 56, a second piping 58, a water sampling valve 60, a watersampler 62, a water storage tank 64, a pump 66, a flow rate adjustmentvalve 68, and a flowmeter 70.

The mixed gas supply part 52 is a member supplying the mixed gas to thetreatment tank 54. The mixed gas supply part 52 includes an ammoniasupply source 72, a nitrogen supply source 74, a mixing ratio adjustmentvalve 76, a supply piping 78, and a fine bubble generating part 80.

The mixed gas supply part 52 uses the ammonia supply source 72 and thenitrogen supply source 74 to generate the mixed gas obtained by mixingammonia (the first gas) and nitrogen (the second gas). The mixingproportions of ammonia and nitrogen can be set to any ratio by themixing ratio adjustment valve 76. The mixed gas is supplied through thesupply piping 78 to the fine bubble generating part 80 disposed in abottom portion of the treatment tank 54. The fine bubble generating part80 is a member forming fine bubbles of the mixed gas.

The treatment tank 54 is a tank (hard water storage part) storing hardwater as treated water to be treated. By supplying the fine bubbles ofthe mixed gas into the hard water in the treatment tank 54, the metalcomponent is removed, or particularly, crystallized, from the hardwater, in accordance with the principle described in the thirdembodiment. The treated water after treatment is sent to the firstpiping 56. The water sampling valve 60 is disposed in the middle of thefirst piping 56. By opening and closing the water sampling valve 60, thetreated water passing through the first piping 56 is sampled. Thesampled treated water is put into the water sampler 62.

The first piping 56 is connected to the water storage tank 64. The waterstorage tank 64 is a tank storing the treated water. The treated waterstored in the water storage tank 64 is returned through the secondpiping 58 to the treatment tank 54. As a result, the treated water iscirculated.

The pump 66, the flow rate adjustment valve 68, and the flowmeter 70 areattached to the second piping 58. The pump 66 is a member generating apropulsive force causing the treated water in the water storage tank 64to flow through the second piping 58. The flow rate adjustment valve 68is a valve adjusting the flow rate of the treated water passing throughthe second piping 58. The flowmeter 70 is a device measuring the flowrate of the treated water flowing through the second piping 58.

The apparatus 50 as described above was used for performing a treatmentof removing the metal component in the hard water in the treatment tank54 while continuously operating the pump 66 and for collecting thetreated water after the treatment from the water sampler 62 to measurevarious parameters. In Experimental Examples 2 to 4, a rate ofcrystallization of the metal component contained in the treated water(crystallization rate) was examined. The crystallization rate in thisspecification is not limited to a substance composed of atoms andmolecules periodically arranged with regularity and means a rate of asubstance simply deposited as a solid. The crystallization rate may bereferred to as “deposition rate”.

FIG. 12 shows an example of a result when the treated water actuallytreated in Experimental Examples 2 to 4 is observed with a scanningelectron microscope (SEM). As shown in FIG. 12, a multiplicity ofcrystals 84 is deposited in treated water 82.

In Experimental Examples 2 and 3, hard water 1 was used as the treatedwater to be treated. The hard water 1 is Evian (registered trademark)having the hardness of about 300 mg/L. In Experimental Example 4, twotypes of hard waters 1 and 2 were used. The hard water 2 is Contrex(registered trademark) having the hardness of about 1400 mg/L.

Experimental Example 2

In Experimental Example 2, the apparatus 50 described above was used forcollecting the treated water after the elapse of a predetermined time assample water with the water sampler 62 while operating the pump 66 tocause the hard water to flow into the treatment tank 54. In ExperimentalExample 2, the mixing proportions of ammonia and nitrogen in the mixedgas were changed to examine differences in the crystallization rate atrespective mixing proportions. Specific experimental conditions ofExperimental Example 2 are listed below. In Experimental Example 2, thetreated water supplied from the treatment tank 54 to the first piping 56was discarded except the water collected with the water sampler 62 andwas not supplied to the water storage tank 64.

Experimental Conditions

-   -   Type of treated water hard water 1    -   Mixing percentage of ammonia in mixed gas: 0% (nitrogen only),        30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% (ammonia only)    -   Flow rate of treated water 2.6 L/min    -   Flow rate of mixed gas: 0.03 min    -   Time from start of operation of pump to collection: 3 minutes    -   Measurement items of sample water pH, Ca hardness (mg/L), total        carbonic acid concentration (mg/L)

For the measurement items of the sample water, the collected samplewater was filtered to remove crystals of the metal component depositedin the sample water before performing the measurement. The Ca hardnessis a value obtained by converting the content of Ca²⁺ contained in thetreated water per unit volume into calcium carbonate (CaCO₃).Commercially available respective measurement devices were used formeasuring the pH, Ca hardness, and total carbonic acid concentration.

Experimental results of Experimental Example 2 are shown in FIGS. 13Aand 13B.

In FIG. 13A, the horizontal axis represents the mixing percentage (%) ofammonia in the mixed gas, and the vertical axis represents thecrystallization rate (%) of the sample water. In FIG. 13B, thehorizontal axis represents the pH of the sample water, and the verticalaxis represents the crystallization rate (%) of the sample water.

The “crystallization rate” was calculated by (the Ca hardness of thesample water before operation—the Ca hardness of the sample water afteroperation)/the Ca hardness of the sample water before operation. Thecrystallization rate calculated in this way represents how many metalions are crystallized in the sample water per unit volume. A highercrystallization rate indicates that more metal ions are crystallizedfrom the sample water.

As shown in FIGS. 13A and 13B, the crystallization rate increases as themixing percentage of ammonia becomes higher. Particularly, when themixing percentage of ammonia is 70% or more, the crystallization ratedramatically increases.

As shown in FIGS. 13A and 13B, it can be seen that when the mixingpercentage of ammonia is higher, the pH is increased. It is noted thatalthough the pH is increased, the maximum value is between 8.5 and 9.The pH reference value for tap water defined by the Ministry of Health,Labor and Welfare is in the range of 5.8 to 8.6, and it can be seen thateven if the mixing percentage of ammonia is high, the pH varies to avalue close to the range. Additionally, the desirable drinkable range ofalkali ion water prescribed in Pharmaceutical Affairs Law is pH 9 to 10.Since the pH value can be kept lower than this range, it can be seenthat the water is suitable as drinking water.

The factor preventing the pH from excessively increasing even at a highmixing percentage of ammonia is probably that the pH is mainly locallyincreased around the fine bubbles 40 as described above with referenceto FIG. 10, rather than increasing the pH of the entire treated water.

Experimental Example 3

In Experimental Example 3, as in Experimental Example 2, the apparatus50 described above was used for collecting the treated water after theelapse of a predetermined time as sample water with the water sampler 62while operating the pump 66 to cause the hard water to flow into thetreatment tank 54. In Experimental Example 3, only two patterns of 70%and 100% were used for the mixing percentage of ammonia in the mixedgas. Unlike Experimental Example 2, the sample water was collected atpredetermined intervals from the start of operation of the pump 66 tomeasure various parameters. Furthermore, unlike Experimental Example 2,the treated water supplied from the treatment tank 54 to the firstpiping 56 was all returned to the water storage tank 64 to circulate thetreated water except the water collected with the water sampler 62.Specific experimental conditions of Experimental Example 3 are listedbelow.

Experimental Conditions

-   -   Type of treated water hard water 1    -   Mixing percentage of ammonia in mixed gas: 70%, 100% (ammonia        only)    -   Flow rate of treated water 2.6 L/min    -   Flow rate of mixed gas: 0.03 L/min    -   Measurement items of sample water pH, Ca hardness (mg/L), total        carbonic acid concentration (mg/L)

Experimental results of Experimental Example 3 are shown in FIGS. 14A,14B, and 14C.

In FIG. 14A, the horizontal axis represents the operating time (minutes)of the pump 66, and the vertical axis represents the crystallizationrate (%) of the sample water. In FIG. 14B, the horizontal axisrepresents the operating time (minutes) of the pump 66, and the verticalaxis represents the Ca hardness (mg/L) of the sample water. In FIG. 14C,the horizontal axis represents the operating time (minutes) of the pump66, and the vertical axis represents the pH of the sample water.

As shown in FIG. 14A, the crystallization rate increases as theoperating time elapses, regardless of whether the ammonia mixingpercentage is 70% or 100%. As shown in FIG. 14B, the Ca hardnessdecreases as the operating time elapses. This reveals that the metalcomponent Ca²⁺ dissolved in the hard water is crystallized as CaCO₃ dueto introduction of the fine bubbles using the mixed gas.

On the other hand, the increase speed of the crystallization rate andthe decrease speed of the Ca hardness are faster when the mixingpercentage of ammonia is 100% than when the mixing percentage is 70%.This reveals that ammonia significantly contributes to thecrystallization of Ca² into CaCO₃.

As shown in FIG. 14C, the pH gradually increases as the operating timeelapses, regardless of whether the mixing percentage of ammonia is 70%or 100%. No significant difference is observed in pH value between whenthe mixing percentage of ammonia is 70% and when the mixing percentageis 100%. Even when the operating time of 50 minutes has elapsed, the pHis between 9 and 10 and is not excessively increased. The factormoderating the increase speed of the pH in this way is probably that thepH is mainly locally increased around the fine bubbles 40 as describedabove with reference to FIG. 10, rather than increasing the pH of theentire treated water.

Experimental Example 4

In Experimental Example 4, as in Experimental Examples 2 and 4, theapparatus 50 described above was used for collecting the treated waterafter the elapse of a predetermined time as sample water with the watersampler 62 while operating the pump 66 to cause the hard water to flowinto the treatment tank 54. As in Experimental Example 3, the samplewater was collected at predetermined intervals from the start ofoperation of the pump 66 to measure various parameters. As inExperimental Example 3, the treated water supplied from the treatmenttank 54 to the first piping 56 was all returned to the water storagetank 64 to circulate the treated water except the water collected withthe water sampler 62. On the other hand, in Experimental Example 4, onlyone pattern of 70% was used for the mixing percentage of ammonia in themixed gas. Unlike Experimental Examples 2 and 3, two kinds of hardwaters, i.e., the hard water 1 (hardness: about 300 mg/L) and the hardwater 2 (hardness: about 1400 mg/L), were used as the treated water.Specific experimental conditions of Experimental Example 4 are listedbelow.

Experimental Conditions

-   -   Types of treated water hard water 1, hard water 2    -   Mixing percentage of ammonia in mixed gas: 70%    -   Flow rate of treated water 2.6 L/min    -   Flow rate of mixed gas: 0.03 L/min    -   Measurement items of sample water pH, Ca hardness (mg/L), total        carbonic acid concentration (mg/L)

Experimental results of Experimental Example 4 are shown in FIGS. 15A,15B, 15C, and 15D.

In FIG. 15A, the horizontal axis represents the operating time (minutes)of the pump 66, and the vertical axis represents the crystallizationrate (%) of the sample water. In FIG. 15B, the horizontal axisrepresents the operating time (minutes) of the pump 66, and the verticalaxis represents the Ca hardness (mg/L) of the sample water. In FIG. 15C,the horizontal axis represents the operating time (minutes) of the pump66, and the vertical axis represents the pH of the sample water. FIG.15D is a graph of FIG. 15B in which the total carbonic acidconcentration (mg/L) is added to the vertical axis.

As shown in FIGS. 15A and 15B, in both the hard water 1 and the hardwater 2, the crystallization rate increases and the Ca hardnessdecreases as the operating time elapses. This reveals that the metalcomponent Ca²⁺ dissolved in the hard water is crystallized as CaCO₃ dueto introduction of the fine bubbles using the mixed gas.

As shown in FIGS. 15A and 15C, it can be seen that the increase speed ofthe crystallization rate and the increase speed of the pH aresignificantly different between the hard water 1 and the hard water 2.Specifically, it can be seen that the increase speed of thecrystallization rate and the increase speed of the pH are higher in thehard water 1 than the hard water 2. In this regard, the presentinventors focused attention on “total carbonic acid concentration” andconducted a study based on data shown in FIG. 15D.

As shown in FIG. 15D, the total carbonic acid concentration of the hardwater 1 has a value of 150 to 200 mg/L when the operating time is 50minutes. Therefore, the hard water 1 contains large amounts of HCO andCO₃ ²⁻. When the operating time is 50 minutes, the crystallization rateof the hard water 1 has reached 70 to 80% as shown in FIG. 15A. On theother hand, the total carbonic acid concentration of the hard water 2has value of about 20 mg/L when the operating time is 70 minutes. Ascompared to the hard water 1, it can be seen that the contents of HCO₃ ⁻and C₃ ²⁻ are significantly smaller in the hard water 2. According tothe data shown in FIG. 15A, the crystallization rate of the hard water 2is expected to be about 40% when the operating time is 70 minutes.

As described in the principles of the first to third embodiments, HCO₃ ⁻and CO₃ ²⁻ function as components for crystallizing Ca²⁺ as CaCO₃. It isprobable that the increase speed of the crystallization rate is higherin the hard water 1 than the hard water 2 since HCO₃ and CO₃ ²⁻ arecontained in larger amounts.

Table 1 shows contents of metal components contained in the hard waters1, 2 and the total carbonic acid concentration.

TABLE 1 amount of CO₃ ²⁻ required for surplus content (mg/L) dissolution(mg/L) amount Ca Mg CO₃ ²⁻ Ca Mg total (mg/L) molecular 40 24.3 60 60weight Contrex 468 74.8 372 702 184.691358 886.691358 −514.691 Evian 8026 357 120 64.19753086 184.1975309 172.8025

As shown in Table 1, the contents of Ca, Mg, and CO₃ ²⁻ per unit volumecontained in the hard water 1, i.e., Evian (registered trademark), are80, 26, and 357 mg/L, respectively. The contents of Ca, Mg, and CO₃ ²⁻per unit volume contained in the hard water 2, i.e., Contrex (registeredtrademark), are 468, 74.8, and 372 mg/L. Therefore, the contents of CO₃²⁻ per unit volume contained in the hard water 1 and the hard water 2are 357 mg/L and 372 mg/L, which are substantially the same. On theother hand, the amount of CO₃ ²⁻ required for dissolution of Ca and Mgrelative to the contents of Ca and Mg contained in hard water is about184 mg/L for the hard water 1 and about 887 mg/L for the hard water 2.Therefore, the hard water 1 has surplus of about 173 mg/L of theactually contained amount of CO₃ ²⁻ relative to the amount of CO₃ ²⁻required for dissolution of Ca and Mg. This means that CO₃ ²⁻ forcrystallizing Ca²⁺ is abundantly present when the fine bubbles of themixed gas are introduced. On the other hand, the hard water 2 is about515 mg/L short of the actually contained amount of CO₃ ²⁻ relative tothe amount of CO₃ ²⁻ required for dissolution of Ca and Mg. As a result,when the fine bubbles of the mixed gas are introduced, crystallizationis probably not promoted due to short of CO₃ ²⁻ for crystallizing Ca²⁺.

From the results described above, it is probable that if the hard waterto be treated abundantly contains carbonic acid such as HCO₃ ⁻ and CO₃²⁻, the increase speed of crystallization can be improved. Based on thisfact, to increase the total carbon dioxide content of the hard water, acarbonic acid gas may be introduced into the hard water beforeintroducing the fine bubbles. Specifically, a carbonic acid gasgenerating part generating a carbonic acid gas may further be included.Before supplying the fine bubbles generated by the fine bubblegenerating part to the hard water, a carbonic acid gas may be generatedby the carbonic acid gas generating part and supplied into the hardwater. This can probably promote the crystallization of the metalcomponent in the hard water.

As described above, according to Experimental Examples 2 to 4, thecrystallization of the metal component can be promoted by setting theamount of substance of ammonia larger than the amount of substance ofnitrogen in the mixed gas. Furthermore, by setting the mixing percentageof ammonia in the mixed gas to 70% or more, the crystallization of themetal component can significantly be promoted.

Experimental Example 5

Experimental example 5 is a sensory evaluation experiment for evaluating“foaming” for the sample water (soft water) treated by using theapparatus 50 described above. The foaming is related to a foaming poweraccording to height and size of foam generated from a water surface. Itis generally considered that when an amount of hardness components issmaller, the foaming is larger, which is advantageous in that a washingeffect is increased when the water is used for the purpose of washing,for example.

In Experimental Example 5, unlike Experimental Examples 2 to 4, finebubbles were generated from a single gas of ammonia instead of the mixedgas. Specifically, in the apparatus 50 shown in FIG. 16, fine bubbleswere generated by using only the ammonia supply source 72 without usingthe nitrogen supply source 74. The method of using the apparatus 50 isthe same as in Experimental Examples 2 to 4 and therefore will not bedescribed.

The experimental method of Experimental Example 5 is based on thestandard of “foaming”: SHASE-S 218 of the Society of Heating,Air-Conditioning and Sanitary Engineers of Japan. Specifically, dilutedwater was prepared by diluting 1.5 g of pure soap with 200 ml of water,and 1 mL of the diluted water and 9 mL of treated water of interest weremixed and put into a measuring cylinder as 10 mL of evaluation water.COW BRAND Soap Red Box a1 (Cow Brand Soap Kyoshinsha Co., Ltd.) was usedfor the pure soap, and distilled water of Autostill WG221 (YamatoScientific Co., Ltd.) was used for 200 ml of water. The measuringcylinder was shaken 50 times, and a height of the foam from the watersurface was measured after 1 minute.

In Experimental Example 5, the same experiment was performed with threetypes of water, i.e., hard water, tap water, and pure water, in additionto the sample water treated by the apparatus 50. Hardnesses of thesewaters and the sample water are as follows.

Hardness of hard water total hardness 300 mg/L, Ca hardness 200 mg/L, Mghardness 100 mg/L

Hardness of tap water total hardness 72 mg/L, Ca hardness 49 mg/L, Mghardness 23 mg/L

Hardness of pure water: total hardness 0 mg/L, Ca hardness 0 mg/L, Mghardness 0 mg/L

Hardness of sample water: total hardness 118 mg/L, Ca hardness 21 mg/L,Mg hardness 97 mg/L

Experimental results of Experimental Example 5 are shown in FIG. 16. InFIG. 16, the horizontal axis represents the type of water, and thevertical axis represents the height (mm) of the foam extending from thesurface of the evaluation water. The vertical axis represents thefoaming and the foaming power.

As shown in FIG. 16, while the “hard water” was highest in both the Cahardnesses and the Mg hardnesses and showed little foaming close to 0,the “tap water”, the “sample water”, and the “pure water” showedapproximately the same high levels of foaming. Therefore, the “samplewater” treated by using the apparatus 50 is improved in terms of foamingas compared to the hard water before treatment and achieves the foamingclose to the “tap water” and the “pure water”. This demonstrates thatthe foaming can be improved by removing the metal ions from the hardwater with the method of the embodiments and that the foaming can beachieved at the same level as tap water and pure water, which are softwater.

Comparing the results shown in FIG. 16 with the specific values of thehardness, when the Ca hardness is lower, the foaming becomes larger.This reveals that the value of the Ca hardness rather than the Mghardness is a dominant parameter having a direct influence on thefoaming.

Experimental Example 6

In Experimental Example 6, the treated water (hard water) is treated byusing the same apparatus 50 (FIG. 11) as in Experimental Examples 2 to 4to compare the crystallization rate of the treated sample water.

In Experimental Example 6, differences in the crystallization rate werecompared between the case of using microbubbles, which are fine bubbles,and the case of using milli-bubbles, which are not fine bubbles.Specifically, in the apparatus 50 shown in FIG. 11, an experiment wasperformed in two patterns by using the fine bubble generating part 80 asit is to generate microbubbles, and by using another bubble generatingpart (not shown) instead of the fine bubble generating part 80 togenerate milli-bubbles.

In Experimental Example 6, unlike Experimental Examples 2 to 4, thebubbles were generated from a single gas of ozone instead of the mixedgas. Specifically, in the apparatus 50 shown in FIG. 11, an ozone supplysource (not shown) was used instead of the ammonia supply source 72 andthe nitrogen supply source 74. As described in Experimental Example 3,the ozone gas is a hydroxyl ion donating gas.

Experimental conditions of Experimental Example 6 are as follows.

-   -   Type of treated water (common): hard water 1    -   Flow rate of treated water (common): 12 L/min    -   Volume of water stored in the treatment tank 54 (common): 9 L    -   Flow rate of ozone gas (common): 0.12 L/min    -   Average bubble diameter of microbubbles: 56 μm    -   Average bubble diameter of milli-bubbles: 1021 μm    -   Measurement items of sample water (common): Ca hardness (mg/L),        total hardness (mg/L)

Experimental results of Experimental Example 6 are shown in FIGS. 17Aand 17B.

In FIG. 17A, the horizontal axis represents the time (minutes), and thevertical axis represents the crystallization rate (%) of the Cahardness. In FIG. 17B, the horizontal axis represents the time(minutes), and the vertical axis represents the crystallization rate (%)of the total hardness.

As shown in FIGS. 17A and 17B, it can be seen that the micro-bubblesachieve higher crystallization rates than the milli-bubbles for both theCa hardness and the total hardness. Therefore, the crystallization rateis higher in the case of using the micro-bubbles, which are the finebubbles, as compared to the case of using the milli-bubbles, which arenot the fine bubbles, and this demonstrates the metal ioncrystallization effect of the fine bubbles.

Experimental Example 7

Experimental Example 7 performed to verify the action of fine bubblespromoting crystallization of metal ions will be described. Experimentswere conducted by using an apparatus 90 shown in FIG. 18.

FIG. 18 is a diagram showing a schematic configuration of an apparatus90 used in Experimental Example 7. The apparatus 90 shown in FIG. 18includes an electrolysis apparatus 91, a first piping 92, a treatmenttank 93, a second piping 94, a pump 95, and a fine bubble generatingpart 96.

The electrolysis apparatus 91 is an apparatus electrolyzing hard waterinto acidic water and alkaline water. Since the electrolysis apparatus91 can substantially increase the pH of the hard water by separating theacidic water from the hard water while leaving the alkaline water. Theacidic water is discharged to the outside of the electrolysis apparatus91. On the other hand, the alkaline water is supplied to the treatmenttank 93 through the first piping 92.

The alkaline water supplied to the treatment tank 93 is supplied throughthe second piping 94 to the fine bubble generating part 96 by drivingthe pump 95. The fine bubble generating part 96 is an apparatussupplying fine bubbles into the alkaline water.

By using the apparatus 90 as described above, the pH of the alkalinewater supplied to the treatment tank 93 was increased to 8.5 or more,and the pump 95 was continuously operated for about 15 minutes toperform a remove treatment for a metal component in the alkaline waterin the treatment tank 93. As a result, it was confirmed that thecrystallization of the metal component in the hard water proceeded untilthe pH of the hard water became 8.3 or less at which the carbonate ionabundance ratio is 1% or less. It was also confirmed that when the pH ofthe alkaline water in the treatment tank 93 is higher than 8.5, thecrystallization of the metal component is promoted (a shorter time and ahigher crystallization rate).

It was confirmed that when the pH of the alkaline water supplied to thetreatment tank 93 was increased to 8.5 or more and then left withoutdriving the pump 95 and the fine bubble generating part 96, the metalcomponent was almost not crystalized.

Fourth Embodiment

An ion removing system according to a fourth embodiment of the presentdisclosure will be described. In the fourth embodiment, differences fromthe first embodiment will mainly be described. In the fourth embodiment,the same or equivalent constituent elements as the first embodiment aredenoted by the same reference numerals. In the fourth embodiment, thedescription overlapping with the first embodiment will not be made.

FIG. 19 is a schematic diagram of an ion removing system according tothe fourth embodiment. The fourth embodiment is different from the firstembodiment in that the return flow path 12 is configured to return aportion of the treated water containing crystals of the metal componentdeposited in the vicinity of the inner circumferential surface 4Aa ofthe separating apparatus 4 to the primary flow path 2.

Specifically, the one end portion 12 a of the return flow path 12 isopened on the inner circumferential surface 4Aa side of the separatingpart 4A. Therefore, the crystals of the metal component deposited in thevicinity of the inner circumferential surface 4Aa are more reliablytaken into the return flow path 12. The connection flow path 3C of theion removing apparatus 3 is connected to the separating part 4A abovethe one end portion 12 a of the return flow path 12. Therefore, the oneend portion 12 a of the return flow path 12 is located below an outletof the connection flow path 3C from which the hard water after removalof the metal ions is spirally discharged downward. As a result, thecrystals of the metal component deposited in the vicinity of the innercircumferential surface 4Aa is more reliably taken into the return flowpath 12.

An inlet of the secondary-side flow path 5 is opened above the one endportion 12 a of the return flow path 12. The inlet of the secondary-sideflow path 5 is disposed at a position distant from the innercircumferential surface 4Aa. As a result, the crystals of the metalcomponent deposited in the vicinity of the inner circumferential surface4Aa are prevented from entering the secondary-side flow path 5.

According to the ion removing system of the fourth embodiment, thecrystals of the metal component can be introduced into the electrolysisapparatus 16 through the return flow path 12. As a result, the metalions use the surfaces of the crystals as starting points for bonding togrow the crystals, so that the crystallization of the metal ions can bepromoted.

The fine crystals of the metal component deposited by the separatingapparatus 4 have a property of being easily dissolved in the treatedwater. On the other hand, according to the ion removing system of thefourth embodiment, the crystals of the metal component are introducedthrough the return flow path 12 into the electrolysis apparatus 16 togrow the crystals of the metal component, so that the dissolution of thecrystals of the metal component can be suppressed.

According to the ion removing system of the fourth embodiment, thesystem includes the pump P causing the hard water flowing through theprimary-side flow path 2 to flow through the electrolysis apparatus 16and the ion removing apparatus 3 to the separating apparatus 4.Therefore, by driving the pump P to forcibly circulate liquid in thecirculation flow path, fluctuations in the flow rate of the liquid canfurther be stabilized to suppress a reduction in the metal ion removalefficiency. Additionally, by forcibly circulating the crystals of themetal component in the circulation flow path, the crystallization of themetal ions can further be promoted.

According to the ion removing system of the fourth embodiment, theclosed-system circulation flow path is made up of the primary-side flowpath 2, the electrolysis apparatus 16, the ion removing apparatus 3, theseparating apparatus 4, and the return flow path 12. As a result, aircan be prevented from being entrapped into the circulation flow path tofurther stabilize the fluctuations in the flow rate of the liquid.

When the metal ions in hard water are Ca²⁺ and Mg²⁺, Ca²⁺ has a positivecharge and a higher ionization tendency than Mg²⁺ and is thereforeadsorbed in preference to Mg²⁺ by OH⁻ present on the surfaces of thefine bubbles due to an action of an intermolecular force (interionicinteraction). Therefore, the crystallization of Mg²⁺ starts at thetiming when the crystallization of Ca²⁺ is completed or almostcompleted. As Ca²⁺ is crystallized and removed from the hard water, thenegative charges present on the surfaces of the fine bubbles decrease,and the PH of hard water is reduced. As a result, the power ofadsorption of Mg²⁺ by the fine bubbles decreases, which makes itdifficult to crystallize and remove Mg²⁺.

On the other hand, according to the ion removing system of the fourthembodiment, the electrolysis apparatus 16 is located in the circulationflow path, so that even if the pH of the hard water decreases due to thecrystallization of Ca²⁺, the pH of the hard water can be increased. As aresult, the power of adsorption of Mg²⁺ by the fine bubbles can beincreased to improve the Mg²⁺ removal efficiency.

The present disclosure is not limited to the embodiments described aboveand can be implemented in various other forms. For example, in the abovedescription, air or nitrogen is used as the ion removal gas in thesoftening treatment; however, the present disclosure is not limitedthereto. A gas other than air or nitrogen may be used as the ion removalgas.

In the above description, carbon dioxide is used as the dissolution gasfor the regeneration treatment; however, the present disclosure is notlimited thereto. For example, the dissolution gas may be hydrogensulfide (H₂S→H⁺+HS⁻) or hydrogen chloride (HCL→H⁺+CL⁻), which is a gasproducing hydrogen ions when dissolved in water.

In the above description, the dissolution gas is used as an example ofthe solubilizer for the regeneration treatment; however, the presentdisclosure is not limited thereto. For example, a liquid (dissolutionliquid) dissolving the crystals of the metal component may be used asthe solubilizer. Examples of such a liquid include hydrochloric acid,sulfuric acid, citric acid, and ascorbic acid. By using such a liquid,the size of the solubilizer supply part 8 can be reduced. Additionally,the frequency of replacement of the solubilizer can be reduced. When aliquid is used as the solubilizer, this can prevent a gas from enteringthe pump P and therefore can eliminate the need for disposing thesolubilizer supply part 8 downstream of the pump P in the flow directionof the hard water. Therefore, the solubilizer supply part 8 may bedisposed in a circulation flow path made up of the primary-side flowpath 2, the ion removing apparatus 3, the separating apparatus 4, andthe return flow path 12. Even with this configuration, the solubilizercan be supplied to the separating apparatus 4 to dissolve the crystalsattached to the separating apparatus 4 for performing the regenerationtreatment.

In the above description, the separating apparatus 4 is the cyclone-typecentrifugal separating apparatuses; however, the present disclosure isnot limited thereto. For example, the separating apparatus 4 may bewater purification filters such as a hollow fiber membrane.

In the above description, only the fine bubbles containing the ionremoval gas are supplied into the hard water; however, the presentdisclosure is not limited thereto. For example, another gas may besupplied in addition to the fine bubbles containing the ion removal gasinto the hard water. In this case, the other gas may be supplied as finebubbles into the hard water or may be supplied as ordinary bubbles intothe hard water.

In the above description, the electrolysis apparatus 16 is configured todischarge the acidic water separated from the hard water to the outsidethrough the discharge flow path 16 a; the present disclosure is notlimited thereto. For example, as shown in FIG. 20, an acidic waterstorage part 101 storing the acidic water generated by the electrolysisapparatus 16 may be connected to the outlet of the discharge flow path16 a. An acidic water flow path 102 allowing the acidic water stored inthe acidic water storage part 101 to flow to the ion removing apparatus3 and an opening/closing valve 103 opening/closing the acidic water flowpath 102 may further be included. In the configuration example shown inFIG. 18, the acidic water flow path 102 is connected to a portiondownstream of the electrolysis apparatus 16 in the flow direction of thehard water and upstream of the ion removing apparatus 3 in the flowdirection of the hard water in the primary flow path 2. Theopening/closing operation of the opening/dosing valve 103 is controlledby the controller 6. According to this configuration, for example, whenthe hard water storage part 3A is washed, the acidic water stored in theacidic water storage part 101 can be allowed to flow as wash water tothe hard water storage part 3A through the acidic water flow path 102,so that the acidic water can effectively be used.

In the above description, the opening/closing operations of the firstvalve 15A, the second valve 15B, and the third valve 15C areautomatically controlled by the controller 6; however, the presentdisclosure is not limited thereto. The opening/closing operations of thefirst valve 15A, the second valve 15B, and the third valve 15C maymanually be performed.

In the case described above, the fine bubbles used are obtained bymixing the two types of gases, i.e., the first gas that is a basic gasand the second gas that is a gas having a property of slower dissolutionrate than the first gas; however, another gas may be mixed in additionto these two types of gases. Therefore, the fine bubbles of a mixed gasobtained by mixing two or more types of gases including the first gasand the second gas may be used.

It is noted that any of the various embodiments and modificationsdescribed above can appropriately be combined to produce the effects ofthe respective embodiments.

Although the present disclosure has been sufficiently described in termsof preferable embodiments with reference to the accompanying drawings,various modifications and corrections are apparent to those skilled inthe art. It should be understood that such modifications and correctionsare included in the present disclosure without departing from the scopeof the present disclosure according to the accompanying claims. Changesin combinations and orders of elements in the embodiments may beachieved without departing from the scope and the idea of the presentdisclosure.

INDUSTRIAL APPLICABILITY

The ion removing system according to the present disclosure is excellentin maintainability and environmental properties and is therefore usefulfor both a household ion removing system and an industrial ion removingsystem.

REFERENCE SIGNS LIST

-   1 ion removing system-   2 primary-side flow path-   3 ion removing apparatus-   3A hard water storage part-   3B fine bubble generating part-   3C connection flow path-   4 separating apparatus-   4A separating part-   4Aa inner circumferential surface-   4B crystal storage part-   4Ba discharge flow path-   5 secondary-side flow path-   6 controller-   7 ion removal gas supply part-   8 solubilizer supply part-   9 gas switching mechanism-   10 opening/closing valve-   11 discharge-side backflow prevention mechanism-   12 return flow path-   13 supply-side backflow prevention mechanism-   14 bypass flow path-   15A first valve-   15B second valve-   15C third valve-   16 electrolysis apparatus-   16 a discharge flow path-   17 opening/closing valve-   18 discharge-side backflow prevention mechanism-   20 apparatus-   21 hard water-   22 water tank-   22 a bottom surface-   22 b water surface-   24 gas supply part-   25 first piping-   26 fine bubble generating part-   27 second piping-   28 pump-   30 first water intake part-   32 second water intake part-   34 metal ion concentration detector-   40 fine bubble-   42 crystal-   D1 distance from first water intake part to second water intake part-   50 apparatus-   52 mixed gas supply part-   54 treatment tank-   56 first piping-   58 second piping-   60 water sampling valve-   62 water sampler-   64 water storage tank-   66 pump-   68 flow rate adjustment valve-   70 flowmeter-   72 ammonia supply source-   74 nitrogen supply source-   76 mixing ratio adjustment valve-   78 supply piping-   80 fine bubble generating part-   82 treated water-   84 crystal-   90 apparatus-   91 electrolysis apparatus-   92 first piping-   93 treatment tank-   94 second piping-   95 pump-   96 fine bubble generating part-   101 acid water storage part-   102 acid water flow path-   103 opening/closing valve

1. An ion removing system comprising: an electrolysis apparatuselectrolyzing hard water to generate acidic water and alkaline water;and an ion removing apparatus that comprises a hard water storage partstoring the alkaline water generated by the electrolysis apparatus and afine bubble generating part generating and supplying fine bubbles to thehard water storage part and that causes the fine bubbles to adsorb metalions in the alkaline water in the hard water storage part to remove themetal ions from the alkaline water.
 2. The ion removing system accordingto claim 1, further comprising: an acidic water storage part storing theacidic water generated by the electrolysis apparatus, an acidic waterflow path allowing the acidic water stored in the acidic water storagepart to flow to the ion removing apparatus, and an opening/closing valveopening/closing the acidic water flow path.
 3. The ion removing systemaccording to claim 1, further comprising: a primary-side flow pathconnected to the ion removing apparatus to supply the hard water to theion removing apparatus; a separating apparatus connected to the ionremoving apparatus and separating crystals of a metal componentdeposited by crystallizing the metal ions removed from the alkalinewater by the ion removing apparatus; a secondary-side flow pathconnected to the separating apparatus to take out, from the separatingapparatus, treated water obtained by separating the crystals; and areturn flow path connected to the separating apparatus to return aportion of the treated water containing the crystals to the primary-sideflow path.
 4. The ion removing system according to claim 3, furthercomprising a pump causing the hard water flowing through theprimary-side flow path to flow through the electrolysis apparatus andthe ion removing apparatus to the separating apparatus.
 5. The ionremoving system according to claim 3, wherein a closed-systemcirculation flow path is made up of the primary-side flow path, theelectrolysis apparatus, the ion removing apparatus, the separatingapparatus, and the return flow path.
 6. The ion removing systemaccording to claim 3, wherein the separating apparatus is a cyclone-typecentrifugal separating apparatus having a tapered inner circumferentialsurface with a diameter decreasing downward and causing the alkalinewater to spirally flow downward along the inner circumferential surfaceso that the crystals are separated.
 7. The ion removing system accordingto claim 6, wherein one end portion of the return flow path is opened onthe inner circumferential surface side of the separating apparatus. 8.The ion removing system according to claim 6, wherein the ion removingapparatus comprises a connection flow path connected to the separatingapparatus above the one end portion of the return flow path.